Probe card assembly

ABSTRACT

The disclosure describes a probe card assembly for nondestructive integrated circuit testing. The probe card assembly includes an outer gimbal bearing with a tapered bearing surface being mounted on a top surface of a printed circuit board. The probe card assembly further includes an inner gimbal bearing with a spherical bearing surface which contacts the tapered bearing surface of the outer gimbal bearing at a single point of contact about a circumference thereof. The probe card assembly further includes a spring plate mounted to the outer gimbal bearing, providing a downward force to a substrate.

FIELD OF THE INVENTION

The invention relates to a self-planarizing probe card assembly and,more particularly, to a probe card assembly for nondestructiveintegrated circuit testing.

BACKGROUND

Wafer-level testing is a critical process to ensure that integratedcircuits and semiconductor devices properly function. That is,wafer-level testing can be used to determine the characteristics orfunctionality of the integrated circuits and semiconductor devices. Theintegrated circuits and semiconductor devices that are being tested aretypically referred to as device(s) under test (DUT).

Wafer-level testing is performed on a probe card assembly of a waferprober. During integrated circuit wafer level test, individualintegrated circuit chips, e.g., DUTs, are tested by temporarilycontacting individual power and signal I/O connections, such as solderbumps, with probes mounted to a probe card assembly of a tester.However, as the number and density of I/Os increase it becomesincreasingly difficult to ensure uniform and low resistance contactbetween the probes and each I/O connection. The probe card assemblyplays a significant role in ensuring this contact.

SUMMARY

In an aspect of the invention, a probe card assembly comprises an outergimbal bearing with a tapered bearing surface mounted on a top surfaceof a printed circuit board. The probe card assembly further comprises aninner gimbal bearing with a spherical bearing surface which contacts thetapered bearing surface of the outer gimbal bearing at a single point ofcontact about a circumference thereof. The probe card assembly furthercomprises a spring plate mounted to the outer gimbal bearing, providinga downward force to a substrate.

In an aspect of the invention, a probe card assembly comprises: an outergimbal bearing mounted on a top surface of a printed circuit board; acompliant interposer positioned within an opening of the outer gimbalbearing and contacting the top surface of the printed circuit board; aninner gimbal bearing positioned within the opening of the outer gimbalbearing; a substrate positioned within an opening of the inner gimbalbearing and in electrical contact with the compliant interposer; and aspring plate mounted to the outer gimbal bearing which is configured toapply downward force directly on a surface of the inner gimbal bearing.

In an aspect of the invention, a probe card assembly comprises: an outergimbal bearing mounted on a top surface of a printed circuit board andan opening with a first profile; a compliant interposer positionedwithin a lower portion of the opening of the outer gimbal bearing; aninner gimbal bearing positioned within an upper portion of the openingof the outer gimbal bearing with a second profile; a mechanism whichprevents rotation of the inner gimbal bearing about a vertical axis; asubstrate positioned within an opening of the inner gimbal bearing andin electrical contact with the compliant interposer; and a spring platemounted to the outer gimbal bearing which is configured to provide adownward force on the inner gimbal bearing and the substrate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention.

FIG. 1 shows an exploded view of a probe card assembly in accordancewith aspects of the present invention.

FIG. 2 shows the probe card assembly in a partially assembled state inaccordance with aspects of the present invention.

FIG. 3 is a cross-sectional view of the probe card assembly along lineA-A of FIG. 2 in accordance with aspects of the present invention.

FIG. 4 shows a cut-away view of a compliant interposer in accordancewith aspects of the present invention.

FIG. 5 shows a partial top down view of the probe card assembly inaccordance with aspects of the present invention.

FIG. 6 shows a top down view of an alternative spring plate assembly inaccordance with aspects of the present invention.

FIG. 7 shows a cross sectional view of the alternative spring plate,taken along line B-B of FIG. 6 in accordance with aspects of the presentinvention.

FIGS. 8A and 8B illustrate the degrees of freedom of a probe cardassembly according to the present invention.

FIG. 9 is a side view diagram of a tester that may be used with theprobe card assembly of the present invention.

DETAILED DESCRIPTION

The invention relates to a self-planarizing probe card assembly and,more particularly, to a probe card assembly for nondestructiveintegrated circuit testing. More specifically, the probe card assemblyof the present invention allows the substrate to tip so it becomesperfectly planar to the device being tested (DUT). In embodiments, theprobe card assembly is configured and structured to interconnect anintegrated circuit chip to a tester for nondestructive integratedcircuit testing. The probe card assembly can be used with differentprobes, e.g., compliant probes, rigid probes, micromachined probes,vertical probes or membrane probes, mounted to the substrate. Inembodiments, the probes should remain in the same location on the probecard so multiple DUTS on the wafer can be tested.

In embodiments, the probe card assembly includes a gimbal bearingassembly mounted on a top surface of a tester interface board. In thisway, the gimbal bearing surfaces can include one spherical (inner)gimbal bearing and one flat, outer gimbal bearing. Advantageously, theconfiguration of the present invention eliminates sticking issuesbetween inner and outer gimbal bearing assemblies, in addition toproviding improved uniform probe contact force to all I/O signal andpower connections for the device(s) under test (DUT). In addition, theprobe card assembly design of the present invention eliminates the needfor cabling and attaching the substrate to the assembly with epoxy, aswell as enables the use of rigid probe systems, compared to compliantprobes which are expensive and limited in ability to connect to closelyspaced solder balls of future products. The present invention alsoprovides a mechanism to fix the substrate to the inner gimbal bearingfor repeatable positioning allowing for thermal expansion of dissimilarmaterials or temperature gradients.

FIG. 1 shows an exploded view of a probe card assembly in accordancewith aspects of the present invention. More specifically, the probe cardassembly 10 includes a printed circuit board 100, e.g., tester interfaceboard, with an outer gimbal bearing 200 mounted on a top surface 100 a.In embodiments, an optional shim 300 can be positioned between the outergimbal bearing 200 and the printed circuit board 100. The shim 300 canhave different thicknesses to accommodate various probe card assemblycomponents as described herein (e.g., substrate, probes, etc.).

In embodiments, the outer gimbal bearing 200 includes an opening 220structured to accommodate a compliant interposer assembly 400. Theopening 220 of the outer gimbal bearing 200 will have a first profile(lower portion) that can constrain movement of the compliant interposer400 in the X and Y directions. In embodiments, dowel pins can be used tosecure the compliant interposer assembly 400 to the outer gimbal bearing200 (as shown in FIG. 7.) In further embodiments, dowel pins can also beused to align and secure the outer gimbal bearing 200 to the printedcircuit board 100. As further described herein, the interposer assembly400 includes a plurality of pins (e.g., spring pins), which electricallyconnect the substrate 600 to the printed circuit board 100.

An inner gimbal bearing 500 is positioned within the opening 220 (with asecond profile, different from the first profile) of the outer gimbalbearing 200. The second profile is a bearing surface which is providedat an upper portion of the opening 220. The inner gimbal bearing 500 canbe provided above a ledge 202 of the outer gimbal bearing 200, formed bythe first profile. In embodiments, the outer gimbal bearing 200 willsubstantially constrain movement of the inner gimbal bearing 500 in theX and Y directions, by way of the profile of the opening 220. Inembodiments, the interposer assembly 400 should be positioned so as tonot interfere with the movement of the inner gimbal bearing 500.

In embodiments, the inner gimbal bearing 500 can include a flexible tab510 which engages the slot 210 of the outer gimbal bearing 200, thuspreventing rotation about the vertical or Z axis. In furtherembodiments, the flexible tab 510 can be positioned in respectivelyaligned slots of the outer gimbal bearing 200 and the inner gimbalbearing 500. The flexible tab 510 can be steel spring or other flexiblematerial, with a stiffness that allows vertical movement in the Zdirection. As described further herein, the flexible tab 510 and slot210 can be replaced with another mechanism to prevent rotation, as shownin FIGS. 6 and 7.

Still referring to FIG. 1, the substrate 600 is positioned within anopening 520 of the inner gimbal bearing 500. In embodiments, thesubstrate 600 can have a pedestal configuration (raised center portion)in order to ensure that it extends above a spring plate 700. The opening520 has a substantially same profile as the substrate 600, whichrestrains movement or rotation of the substrate 600 with respect to theinner gimbal bearing 500. The opening 520 further permits the substrate600 to contact the plurality of pins (e.g., spring pins) of theinterposer 400, thus facilitating the connection of the substrate 600 tothe printed circuit board 100. In this way, it is possible to have anelectrical connection between the substrate 600 and the printed circuitboard 100 via the pins of the compliant interposer 400. The substrate600 may be ceramic or organic materials or a composite material.

The spring plate 700 is attached (mounted) to the outer gimbal bearing200 surrounding the inner gimbal bearing 500. In embodiments, the springplate 700 includes an opening 710 which exposes a surface of thesubstrate 600, e.g., raised area which will seat within the opening. Inthe configuration shown in FIG. 1, an underside of the spring plate 700will provide a downward force directly on the substrate 600 and, inembodiments, the inner gimbal bearing 500. This downward force willcompress the pins of the interposer 400 between the substrate 600 andthe printed circuit board 100 thus ensuring a uniform and fullycompliant connection therebetween, e.g., electrical connections of thesubstrate fully contacting the respective pins of the interposer 400.Compliance of the interposer 400 allows the substrate 600 to tilt; thatis, as the inner gimbal bearing 500 tilts, the compression of theinterposer 400 as applied by the substrate 600 will increase on one sideand decrease on another side.

Also, the spring plate 700, which is connected to the outer gimbalbearing 200, will urge the inner gimbal bearing 500 into contact withthe outer gimbal bearing 200 while allowing the substrate 600 and thusthe probes that are attached to it to dynamically maintain planarity tothe device being tested (DUT). The initial difference in planaritybetween the probes and the DUT should be less than the acceptable rangeof compression of the interposer. In embodiments, the spring plate 700can be an assembly of different parts, including a frame and a stainlesssteel, hardened steel or other appropriate spring type material.

FIG. 2 shows the probe card assembly 10 in a partially assembled statein accordance with aspects of the present invention. More specifically,FIG. 2 shows the outer gimbal bearing 200 and inner gimbal bearing 500mounted on the top surface of the printed circuit board 100. Thesubstrate 600 is held within the inner gimbal bearing 500 and, inembodiments, within the spring plate 700. The spring plate 700 ismounted to the outer gimbal bearing 200, thereby holds the assemblytogether.

As previously described, the spring plate 700 will provide a downwardforce onto the substrate 600 and the inner gimbal bearing 500. Thisdownward force will compress the pins of interposer between thesubstrate 600 and the printed circuit board 100 ensuring a uniform andfully compliant connection therebetween. Also, the spring plate 700 andits connection to the outer gimbal bearing 200 will provide ample spaceto allow each side (e.g., right side and left side) of the inner gimbalbearing 500 to tilt from side-to-side in the vertical direction. Thisfloating feature ensures that the substrate 600 is fully compliant(e.g., in contact) with the pins of the interposer (not shown).

As further shown in FIG. 2, the spring plate includes an opening 710which restrains the substrate 600 from any rotational movement, e.g.,about the Z axis. That is, in embodiments, the opening 710 has a profilewhich will mate or contact with flat corners of the substrate 600;although other configurations are also contemplated by the presentinvention. For example, the opening 710 can have straight sides whichcontact the straight sides of the substrate 600. In any suchconfiguration, though, the spring plate 700 (and the opening of theinner gimbal bearing) will prevent certain movements, e.g., a rotationabout the Z axis, of the substrate 600.

FIG. 3 is a cross-sectional view of the probe card assembly 10 alongline A-A of FIG. 2. In this view, the interposer 400 is shown to beprovided within the opening 220 of the outer gimbal bearing 200. Theinterposer 400 is also provided between the substrate 600 and theprinted circuit board 100, with a downward force being applied by thespring plate 700. The inner gimbal bearing 500 is mounted within theopening 220 of the outer gimbal bearing 200.

In one contemplated embodiment, the bearing surfaces of the inner gimbalbearing 500 and the outer gimbal bearing 200 can have a same profile,e.g., spherical. Also, in embodiments, the inner gimbal bearing 500 canrotate about a center point which is at the tip of the probe and thecenter or substantially the center of the substrate 600. In other words,the geometric center of the spherical bearing's surface is near thecenter of the probe array. This allows the substrate 600 to tip aboutthe X and Y axes, without causing any misalignment in the X and Ydirections. In other embodiments, the center of the spherical surfacemay be slightly above or below the tips of the probes causing the probeto scrub on the solder balls or pads of the substrate as the substratetilts.

In alternative embodiments as shown in the exploded view of FIG. 3, theinner edge surface (bearing surface) 200 a of opening 220 of the outergimbal bearing 200 and the outer edge surface (bearing surface) 500 a ofthe inner gimbal bearing 500 have different profiles. For example, theinner edge surface 200 a of opening 220 of the outer gimbal bearing 200has a conical or tapered profile; whereas, the outer edge surface 500 aof the inner gimbal bearing 500 has a spherical profile. In this way,the inner edge surface 200 a of opening 220 of the outer gimbal bearing200 is tangent to the outer edge surface 500 a of the inner gimbalbearing 500. By using such a configuration, there is a single point ofcontact “C” between the two edges or surfaces, which will minimize anyfrictional forces between the surfaces 200 a and 500 a and reduce anysticking between the outer gimbal bearing 200 and the inner gimbalbearing 500. Also, the inner gimbal bearing 500 can be provided abovethe ledge 202 of the outer gimbal bearing 200, formed by the firstprofile. The substrate 600 also rests on a ledge 404 of the inner gimbalbearing 500 to control the height of the substrate and support verticalforces.

In embodiments, the outer gimbal bearing 200 can also have a coating orlubrication, e.g., Polytetrafluoroethylene (PTFE) which has a brand nameof Teflon® (Teflon is a registered trademark of DuPont Co.). The coatingcan reduce friction between the outer gimbal bearing 200 and the innergimbal bearing 500, and hence assist in preventing sticking issues.

FIG. 4 shows a cut-away view of a compliant interposer 400 in accordancewith aspects of the present invention. As shown in this view, thecompliant interposer 400 includes a plurality of pins 410 which canfloat in respective openings of the compliant interposer 400. Inembodiments, the plurality of pins 410 can be spring or pogo pins, as anexample, made from a conductive material, e.g., copper, nickel or goldplated material. Other types of interposers are also contemplated by thepresent invention with different configurations and pins such as, forexample, interposers with conductive polymer bumps, isotropic conductivesheets, etc.

Also, a center support post (rigid or compliant post) 420 can beprovided at the center of the compliant interposer 400. In this way, thecenter of the substrate can rest on the center support post 420,facilitating the tilting motion. The center support post 420 should beof such a height from the surface as to not interfere with any of theconnections between the plurality of pins 410 and the substrate. Thatis, in embodiments, the center support post 420 should equal the heightof the pins 410 when the pins are in a compressed state. The compliantinterposer 400 is preferably made from a rigid material (e.g., plastic)or assembly thereof.

In embodiments, the center support post 420 supports the substrate 600in the vertical direction, while allowing the substrate 600 to gimbal.In embodiments, the center support post 420 will provide additionalsupport at the center of the substrate 600 and reduce the tendency ofconcave bowing. In one embodiment, the bearing surface of the outerbearing is vertical, providing alignment in the XY direction. In thiscase, all downward force from the probes and spring will be supported bythe interposer and center support post 420.

FIG. 5 shows a partial top down view of the probe card assembly 10 inaccordance with aspects of the present invention. As shownillustratively in this view, the inner gimbal bearing 500 includes aspring feature 520. Advantageously, the spring feature 520 cancompensate for misalignment of the substrate 600 due to tolerancesand/or thermal coefficient of expansion (CTE) mismatch between thecomponents of the probe card assembly 10, e.g., outer gimbal bearing200, inner gimbal bearing 500 and substrate 600. In this way, the springfeature 520 can adjust the position of the substrate 600 into properalignment with the interposer, for example. Also, the spring feature 520will ensure that the substrate 600 remains in position during testing ofall DUTs on the wafer.

In embodiments, the spring feature 520 can be composed of a portion ofthe frame of the inner gimbal bearing 500, as defined by a slot 530 anda set screw 540. As should be understood by those of skill in the art,the spring feature 520 can be used to position the substrate 600 withinthe opening 500 a of the inner gimbal bearing 500, in the X and Ydirection (e.g., towards the opposite sides of the opening). Inembodiments, the set screw 540 can be used to adjust the pressureimposed by the spring feature 520 on the substrate 600. FIG. 5 alsoshows the flexible tab 510 keyed into the slot 210 of the outer gimbalbearing 200. In this way, the inner gimbal bearing 500 and substrate600, which is held in the inner gimbal bearing 500, will be preventedfrom any rotation about the vertical axis (Z axis).

FIGS. 6 and 7 show an alternative spring plate in accordance withaspects of the present invention. More specifically, FIG. 6 is a topdown view of the alternative spring plate 700′; whereas, FIG. 7 is across sectional view of the alternative spring plate 700′, taken alongline B-B of FIG. 6.

As shown in FIG. 6, for example, the spring plate 700′ includes aslotted configuration 720. In embodiments, the slotted configuration canbe of different patterns. For example, the pattern can be a serpentineconfiguration. The different patterns (e.g., serpentine configuration)720 can flex or move in multi-directions, thus compensating fortolerances in the X-Y directions and allowing movement in the Zdirection for compliance and tilting of the underlying substrate 600. Inembodiments, the spring plate 700′ will be mounted directly to the outergimbal bearing 200, with the serpentine configuration 720 over the innergimbal bearing 500. This configuration provides the requisite downwardforce on the substrate 600 (by virtue of its mounting to the innergimbal bearing 500) so that it can be fully compliant with theconnections (pins) of the interposer 400.

As further shown in FIGS. 6 and 7, the substrate 600 can be mounted tothe inner gimbal bearing 500, e.g., by one or more screws “S”. This willensure that the substrate 600 stays fully constrained within the innergimbal bearing 500, and hence will move in unison with the movement ofthe inner gimbal bearing 500. In this configuration, the substrate 600is an organic substrate. As further shown in FIGS. 6 and 7, the springplate 700′ is mounted to the outer gimbal bearing 200, e.g., by one ormore screws “S”, with the serpentine configuration 720 provided over thecircumference of the inner gimbal bearing 500. This configurationprovides the necessary downward force.

As shown in FIG. 7, a dowel 800 is used to secure and align theinterposer assembly 400 to the outer gimbal bearing assembly 200. A shim750 can also be placed between the inner gimbal bearing 500 and thesubstrate 600 to reduce stress on the assembly. The shim 750 oradjustment features such as screws can be installed at various locationsin the assembly to adjust for manufacturing tolerances and assure thereis sufficient force on the interposer for reliable electrical contact atthe same time the inner and outer bearing are in intimate contact.Examples would be between the spring and substrate, between the springand outer bearing and between the outer bearing and board.

Dowel pins are commonly used to align different components of probe cardassemblies. For delicate parts that must be assembled by hand the dowelpins need to be made smaller than the hole by some tolerance. If morethan one pin is used the tolerance must be increased to allow formachining errors in the hole locations. Sometimes one hole isintentionally elongated to allow slightly tighter tolerances. Thetolerances tend to increase over time due to wear of the holes and pinsduring assembly and use. The dowel pins 800 of FIG. 7 provide acceptableaccuracy for aligning the pogo pins of the interposer 400 to therelatively large pads on the substrate 600 via the outer bearing 200.

As the DUT solder ball size and spacing continue to decrease, animproved method of alignment is needed to hold the probes in alignmentwith the solder balls after testing multiple chips on a wafer. As shownin FIG. 7, a set screw or other raised feature of the inner bearingrepresented at reference numeral 740 engages the slots 730 of theserpentine configuration 720 thereby preventing rotation about the Zaxis (thus eliminating the need for the flexible tab configuration),while still allowing a tilting movement of the inner gimbal bearing 500and substrate 600. In embodiments, the set screw 740 can have a wedgeshape, a conical shape, spherical shape or other shape that would engagewith the slots 730. The spring forces the screw tip into the slot thusassuring perfect repeatable alignment regardless of small variations inthe shape or locations of the screw or slot due to initial fabricationor wear of the parts.

In embodiments, a wedge shape of the set screw which engages the slots730 will prevent the screw from rotation and hence disengaging from theslots. Also, the wedge shape would provide a line contact into the slots730 thus making it more durable. In any of these configurations, theflexible tab configuration shown in FIGS. 1 and 5 can be eliminated. Inembodiments, the set screw 740 can be placed on any combination of sidesof the serpentine configuration 720 to engage with the slots 730. Asfurther shown in FIG. 7, the set screw 740 can be part of an assembly ofthe inner gimbal bearing 500. The set screw 740 engaging the serpentineconfiguration 720 can also be used to adjust the initial planarity ofthe substrate 600.

In alternate embodiments, the set screw 740 can be a raised area of theinner gimbal bearing 500 or the spring plate 700′, where the slots 730can be a depressed area in the other of the gimbal bearing 500 or thespring plate 700′ such that the raised area contacts with a portion ofthe depressed area by the spring force in order to prevent rotationabout the Z axis. In embodiments, the raised and/or depressed areas havea tapered or curved shape.

Other configurations will now be obvious, for example, a conical shapepin forced into a hole will restrain one more degree of freedom. Acylindrical post can be forced into a tapered hole or slot. The hole orslot can be formed on the inner bearing or substrate with the conicalsurface formed on the spring. Springs can be configured to havedifferent stiffness in different directions, for example a simplecantilever flat sheet metal spring will have little stiffness in thedirection of the thickness but high stiffness in the direction of itslength and width. Springs can be strait or curved and fixed at one endor both ends. The preferred spring plate 700′ is a serpentine patternfixed at both ends.

In embodiments, the vertical forces in the assembly need to be balanced.In one example, for a very large chip, the probe force may be 400 pounds(lbs.), with the interposer force being only 75 lbs. at its recommendedcompression. In this case, the spring force may be designed to be 100lbs. to insure good contact between the inner gimbal bearing 500 and theouter gimbal bearing 200 when the probes are being aligned to the DUT.During probing, the resulting force of 400 lbs.+100 lbs.−75 lbs.=425lbs. is supported by the bearing surface of the inner gimbal bearing500, e.g., spherical bearing surface. The bearing geometry, bearingsurfaces and substrate all need to be designed to support this loadwithout excessive deflection.

Also, during probing the perimeter support of the substrate by the innergimbal bearing 500 will result in a tendency of the substrate 600 tobecome bowed creating a concave surface on the substrate resulting inheavier probe marks around the perimeter. In one embodiment, thesubstrate 600 is connected to the inner gimbal bearing 500 by screws “S”on the center of each side. Supporting the substrate 600 at only thesides and not the corners results in reduced bowing of the substrate600. This can be accomplished with a shim 750 that is in the area of thescrews or raised areas on the substrate or bearing. When the probe isbeing aligned the force from the interposer will tend to cause thesubstrate to bow slightly creating a convex surface.

FIGS. 8A and 8B illustrate the degrees of freedom of a probe assemblyaccording to aspects of the present invention. FIG. 8A is an isometricview and FIG. 8B is a side view of the substrate 600 in accordance withaspects of the present invention. In FIG. 8A, vertical axis defines theZ-direction, with the X and Y directions being orthogonal to each otherand to the Z direction. The θ direction is defined as rotation about theZ direction. L is a vector to an arbitrary probe tip 450 protrudingabove surface of the substrate 600. In FIG. 8B, the surface of thesubstrate 600 has been tilted through an angle α through an arbitraryaxis 445 (see FIG. 8A). By making such a tilting movement, it ispossible to ensure full compliance and contact of the probe to thesolder ball on the DUT.

FIG. 9 is a side view diagram of a tester that may be used with theprobe card assembly 10 of the present invention. As one of skill in theart should realize, the probe card 10 is mounted upside down from theprevious figures. In FIG. 9, a tester 500 includes a test fixture 505, atest controller 506 and an optional compliance controller 507. Testfixture 505 includes a base 510 and a head platen 515 connected to base510 by posts 520. Test fixture 505 further includes a test head 525, anXYZθ stage 530 and a vacuum chuck 535 (e.g., a clamp mechanism may besubstituted) for clamping an integrated circuit wafer 600 having amultiplicity of integrated circuit chips, in place. XYZθ stage 530 ismounted to base 510 and vacuum chuck 535 is mounted to XYZθ stage 530.Test head 525 is mounted to a top surface 540 of head platen 515. Aprobe card assembly 10 is mounted to a bottom surface 545 of test head525. Mounted on probe card assembly 10 is probe assembly 250. Bottomsurface 545 is also the datum of test fixture 505. A multiple electricalconductor cable 550 connects test head 525 to test controller 506.Alternatively, the connection can be made with pogo pins, alsorepresented by reference numeral 550. Multiple electrical conductorcables 555 connect probe card assembly 10 to test head 525. An optionaltube 560 connects optional compliance controller 507 to probe cardassembly 10 in the event that the probe card assembly utilizes acompliance mechanism requiring a pressurizing fluid. In operation, XYZθstage 530 moves integrated circuit chip on wafer 600 under and alignedto probe assembly 10 and then raises the wafer so solder bumps on theintegrated circuit chip contact the probe tips of the probe assembly.The Z-direction travel defines the first order compliance of the tester.

The method(s) as described above is used in the fabrication ofintegrated circuit chips. The resulting integrated circuit chips can bedistributed by the fabricator in raw wafer form (that is, as a singlewafer that has multiple unpackaged chips), as a bare die, or in apackaged form. In the latter case the chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case the chip isthen integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a motherboard, or (b) an end product. The end productcan be any product that includes integrated circuit chips, ranging fromtoys and other low-end applications to advanced computer products havinga display, a keyboard or other input device, and a central processor.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A probe card assembly, comprising: an outergimbal bearing with a tapered bearing surface being mounted on a topsurface of a printed circuit board; an inner gimbal bearing with aspherical bearing surface which contacts the tapered bearing surface ofthe outer gimbal bearing at a single point of contact about acircumference thereof; and a spring plate mounted to the outer gimbalbearing, providing a downward force to a substrate, wherein thespherical bearing surface of the inner gimbal bearing and the taperedbearing surface of the outer gimbal bearing have a different profilesuch that the tapered bearing surface is tangential at a single positionto the spherical bearing surface.
 2. The probe card assembly of claim 1,further comprising a mechanism which prevents rotation of the innergimbal bearing about a vertical axis with respect to the outer gimbalbearing.
 3. The probe card assembly of claim 2, wherein the mechanismcomprises a depressed area provided on one of the spring plate and theinner gimbal bearing which engages with a raised area of another of thespring plate and the inner gimbal bearing to prevent rotation of thesubstrate about a Z-axis.
 4. The probe card assembly of claim 2, whereinthe mechanism includes a flexible tab extending between the inner gimbalbearing and the outer gimbal bearing.
 5. The probe card assembly ofclaim 2, wherein the mechanism includes slots provided on the springplate engaging with at least one set screw provided as an assembly withthe inner gimbal bearing.
 6. The probe card assembly of claim 5, whereinthe at least one set screw has a wedge shape which engages with aslotted pattern of the spring plate.
 7. The probe card assembly of claim6, wherein the slotted pattern is a serpentine configuration, whichflexes when the substrate tilts and restraining a rotation about a Zaxis of the substrate.
 8. The probe card assembly of claim 1, whereinthe inner gimbal bearing includes a spring mechanism to adjust apositioning of the substrate within the opening of the inner gimbalbearing.
 9. The probe assembly of claim 1, further comprising a shimprovided between the substrate and the inner gimbal bearing to reducestresses in the substrate.
 10. A probe card assembly, comprising: anouter gimbal hearing mounted on a top surface of a printed circuitboard; a compliant interposer positioned within an opening of the outergimbal bearing and contacting the top surface of the printed circuitboard; an inner gimbal bearing positioned within the opening of theouter gimbal bearing; a substrate positioned within an opening of theinner gimbal bearing and in electrical contact with the compliantinterposer; and a spring plate mounted to the outer gimbal bearing whichis configured to apply downward force directly on a surface of the innergimbal bearing, wherein an outer edge surface of the inner gimbalhearing and an inner edge surface of the outer gimbal bearing have adifferent profile such that the outer edge surface is tangential at asingle position to the inner edge surface.
 11. The probe card assemblyof claim 10, further comprising a mechanism which prevents rotation ofthe inner gimbal bearing about a vertical axis.
 12. The probe cardassembly of claim 11, wherein: the mechanism includes slots provided onthe spring plate engaging with at least one set screw provided as anassembly with the inner gimbal bearing; the slots of the spring plateare provided in a serpentine configuration above an upper surface of theinner gimbal bearing; and the spring plate provides a downward force onthe substrate, via the substrate's attachment to the inner gimbalbearing.
 13. The probe card assembly of claim 10, wherein the innergimbal bearing includes a spring mechanism to adjust a positioning ofthe substrate within the opening of the inner gimbal bearing.
 14. Theprobe card assembly of claim 10, wherein a bearing surface of the innergimbal bearing and the outer gimbal bearing have a same profile.
 15. Theprobe card assembly of claim 10, wherein the compliant interposerincludes a center post which is structured and positioned to facilitatea tilting motion of the substrate.
 16. A probe card assembly,comprising: an outer gimbal bearing mounted on a top surface of aprinted circuit board and having an opening with a first profile; acompliant interposer positioned within a lower portion of the opening ofthe outer gimbal bearing; an inner gimbal bearing positioned within anupper portion of the opening of the outer gimbal bearing having a secondprofile; a mechanism which prevents rotation of the inner gimbal bearingabout a vertical axis; a substrate positioned within an opening of theinner gimbal bearing and in electrical contact with the compliantinterposer; and a spring plate mounted to the outer gimbal bearing whichis configured to provide a downward force on the inner gimbal bearingand the substrate, wherein a bearing surface of die inner gimbal beatingand bearing surface of the outer gimbal bearing, have a differentcircumferential profile such that the bearing surface of the outergimbal bearing is tangential at a single position to the bearing surfaceof the inner gimbal bearing.
 17. The probe card assembly of claim 16,wherein: the mechanism includes serpentine slots provided on the springplate engaging with at least one set screw provided as an assembly withthe inner gimbal bearing; the serpentine slots of the spring plate areprovided above a circumference of the inner gimbal bearing; and thespring plate provides a downward force on the substrate by contactingthe inner gimbal bearing such that electrical connections of thesubstrate are fully compliant with pins of the interposer.
 18. The probecard assembly of claim 16, wherein the inner gimbal bearing includes aspring mechanism to adjust a positioning of the substrate within theopening of the inner gimbal bearing.